Metal cylinders, particularly steel cylinders, cannot be used to store many reactive gases, since the reactive gas would attack the metal of the cylinder. This is particularly important in certain industries, such as computer chip manufacture, which require very high purity gases during the manufacturing process. It is known to coat the interior of metal cylinders with a plastic coating to prevent attack by reactive gases. The known processes for coating the interior surface of the cylinder utilize a solution or dispersion of a polymeric material, which is sprayed onto the interior surface of the cylinder. The carrier solvent must then be evaporated and removed from the cylinder followed by heat treatment of the cylinder to melt and fuse the polymeric material.
The known spray coating methods for applying a coating of a polymeric material are subject to many problems. Such processes result in the application of a relatively thin, i.e., less than about 1 mm, coating. The relatively thin coating applied by the spray coating process is subject to pinholes due to the out-gassing of the carrier solvent. The metal of the cylinder can be attacked through such pinholes and subsequent failure of the cylinder can result.
The treatment of polymeric materials with fluorine to provide a fluorinated surface on the polymeric material is known. The direct fluorination of the surface of polymeric materials is usually accomplished using a mixture of fluorine and a carrier gas which reduces the aggressiveness of the fluorine. It is known to use nitrogen, helium and argon as the carrier fluid. U.S. Pat. No. 4,994,308, to Tarancon is directed to use of carbon dioxide as a carrier fluid to provide improved efficiency and removal of byproduct hydrogen fluoride.
The present invention is directed to a method for applying a uniform, relatively thick coating of polymeric material on the interior surface of a cylinder. The relatively thick coating of the polymeric material is particularly adapted to be cross-linked and fluoridated to provide improved resistance to attack by reactive gases.
It is therefore an object of the present invention to provide an improved method for applying a coating of a polymeric material onto the interior surface of a cylinder.
It is a further object of the present invention to provide a cylinder which has been coated with a uniform, relatively thick polymeric material which is free of pinholes and which is adapted to contain reactive gases.
It is a still further object of the present invention to provide a cylinder which has been coated with a polymeric material on the interior surface of the cylinder and wherein the treated neck portion of the cylinder is protected from contact with any gas which is stored in the cylinder.
Further objects, features and advantages of the present invention will become more apparent upon consideration of the detailed description of the invention taken in conjunction with the accompanying claims.